The scan, called MRI, can predict the odds of a heart attack or heart-related death in people with chest symptoms, even after accounting for conventional risk factors like high blood pressure, smoking and diabetes. Intriguingly, researchers on a new study said, the device is able to detect reduced blood flow to the crown of the heart that dramatically magnifies the risk of these bad outcomes.
"With the MRI, the pictures are clearer and the spatial resolution is higher" than conventional heart imaging, said Dr. W. Gregory Hundley, a radiologist at Wake Forest University School of Medicine in Winston-Salem, N.C., and leader of the research team. "And one thing we found is the location within the heart of [the blocked blood] appeared to portend a poor prognosis," Hundley said.
The results of the study appear in tomorrow's issue of the journal Circulation: Journal of the American Heart Association.
Unlike other scanners, an MRI takes three-dimensional images. While MRI is now a standard tool for peering at other organs, it has only lately been turned on the heart as a way to assess pumping power, blood flow and other important features. However, experts said the non-invasive test is the future of cardiac screening, thanks to the precision images it provides without radiation or invasive procedures.
The leading method for looking at the heart is echocardiography, which uses sound waves to generate its image of the organ. The test is a good one, both cheap and portable, but it doesn't work particularly well in people who are obese or who smoke, and in 15 percent to 20 percent of patients the resulting pictures are difficult to read.
In the latest study, Hundley's group gave MRI "stress tests" to 279 men and women with cardiovascular disease and poor showings on echocardiography. To simulate the effects of exercise on the heart the patients received injections of the drugs dobutamine and, if necessary, atropine, which cause the organ to beat faster.
As expected, people with severely constricted blood flow, or ischemia, in the heart after the injections had more than three times the risk of a heart attack or sudden heart-related death over the next two years as those with normal results on the stress test. For those whose pumping outflow -- a measure called left ventricular ejection fraction -- was reduced by 40 percent or more vs. normal, the risk of suffering these problems jumped more than fourfold.
In other words, Hundley said, the results demonstrate that MRI can effectively tell doctors which patients are at high risk of serious or fatal heart problems in the future.
Two previous studies had linked problems with the heart's apex -- which normally resembles the point of a football -- to impaired exercise ability and poor prognosis after a heart attack.
Hundley's group was able for the first time to take pictures of damage to the apex, and they found that people with such damage -- the result of a previous heart attack, perhaps -- were six times more likely than those without injury to suffer additional heart attacks or to die of cardiovascular illness.
"When you lose that football shape you get into trouble," said Hundley. Treatment to restore blood flow to the heart may want to focus on the apex, Hundley said, though that needs to be studied further.
MRI isn't for everyone, at least for the moment. The machines don't like metal plates, pacemakers, or defibrillators, so a small percentage of people with heart rhythm anomalies can't undergo the test.
But "it really is turning into something of a revolution in cardiology," said Dr. Dudley Pennell, a heart expert at London's Royal Brompton Hospital and past president of the Society for Cardiovascular Magnetic Resonance. "It's opening up new vistas for us. We can see things we haven't seen before."
Over the last five years, Pennell said, researchers have used MRI to watch blood flow problems in patients with insulin resistance and to gauge the true extent of damage from heart attacks, neither of which was possible without the technology.
Dr. Gerald Pohost, chief of cardiovascular medicine at the University of Southern California's Keck School of Medicine in Los Angeles and an MRI advocate, acknowledged that the scans are more expensive than other heart imaging tools. "But it has great potential to do a lot of things," Pohost said, from generating three-dimensional pictures of the pump to observing how it processes energy.
What To Do
More than 1 million Americans suffer a heart attack every year, and 460,000 die of the episode. For more information about heart attacks and other cardiovascular ailments, try the American Heart Association or the National Heart, Lung, and Blood Institute.